1. Field of the Invention
The present invention relates to an apparatus for controlling the speed of an internal combustion engine vehicle, and more particularly to a vehicle speed control apparatus for an internal combustion engine vehicle in which switching between a manual vehicle speed controlling mode and an automatic vehicle speed controlling mode by means of an automatic vehicle speed controlling device can be smoothly carried out.
2. Description of the Prior Art
Automatic vehicle speed controlling devices have been widely used for the purpose of automatically maintaining the speed of vehicles driven by internal combustion engines, such as diesel engines, gasoline engines and the like at a desired speed. In the internal combustion engine vehicle equipped with such an automatic vehicle speed controlling device, the desired amount of fuel supply corresponding to the amount of depression of an accelerator pedal and the amount of fuel supply required for maintaining the vehicle speed at a desired speed are separately calculated. Then, the larger of the two amounts of fuel supply is selected aand the engine speed is controlled in accordance with control data showing the selected amount of fuel supply.
Therefore, in the conventional automatic vehicle speed controlling device when, for example, the accelerator pedal is deeply depressed at a time when the amount of fuel supply calculated in accordance with the degree of depression of the acceleration pedal is smaller than that calculated by the automatic vehicle speed controlling device because the accelerator pedal has been in the released condition up to that time, the amount of fuel supply calculated in accordance with the degree of the depression of the accelerator pedal increases beyond the amount of fuel supply calculated by the automatic vehicle speed controlling device, so that the vehicle speed is controlled in accordance with the degree of depression of the accelerator pedal.
In addition, in the conventional automatic vehicle speed controlling device, when the vehicle speed controlling state is switched to the mode of control by operation of the accelerator pedal, the amount of fuel supply calculated by the automatic vehicle speed controlling device becomes zero and control of vehicle speed by the automatic vehicle speed controlling device is discontinued until, for example, a predetermined switch is depressed. Such an automatic vehicle speed controlling device is disclosed in, for example, U.S. Pat. No. 4,337,511.
In such a device, the amount of the fuel supply calculated by the automatic vehicle speed controlling device returns to the previous value, when the predetermined switch is depressed after the vehicle speed control mode is changed from control by the automatic vehicle speed controlling device to that by the accelerator pedal, and the accelerator pedal is released. Therefore, especially when the accelerator pedal is released suddenly, there is the disadvantage that the vehicle rapidly decelerates for a moment just after changing to the automatic vehicle speed control mode so that the vehicle does not travel smoothly. This condition will occur in a vehicle driven by any kind of internal combustion engine.